The present invention relates generally to systems for controlling EGR flow and/or turbocharger swallowing capacity/efficiency, and more specifically to systems for providing such control as a function of commanded charge flow and EGR fraction.
Systems for controlling EGR flow and/or turbocharger swallowing capacity are known and have been widely implemented, particularly in the heavy diesel engine industry. An example of one known system 10 for providing such control is shown in FIG. 1 and 10 includes an internal combustion engine 12 having an intake manifold 14 fluidly coupled to a compressor 18 of a turbocharger via intake conduit 16, wherein the compressor 18 receives fresh air via intake conduit 20. The turbocharger compressor 18 is mechanically coupled to a turbocharger turbine 24 via shaft 22, wherein turbine 24 is fluidly coupled to an exhaust manifold 28 of engine 12 via exhaust conduit 30, and is further fluidly coupled to ambient via exhaust conduit 26. An EGR valve 32 is disposed in fluid communication with the intake conduit 16 and the exhaust conduit 30, and a differential pressure sensor, or xcex94P sensor, 34 is disposed across the EGR valve 32 to sense a pressure change, or delta pressure, across valve 32. An electronic EGR flow controller 36 has a first input receiving a signal indicative of desired EGR valve position, and has a first output electrically connected to EGR valve 32 via signal path 38. In the system shown in FIG. 1, the EGR flow controller is configured to apply the EGR position signal directly to the EGR valve 32. Controller 36 includes a second input receiving a signal indicative of a desired delta pressure value, or xcex94P target, and a third input electrically connected to the xcex94P sensor 34 via signal path 40 and receiving a signal thereat indicative of sensed delta pressure (xcex94P). The xcex94P value is subtracted from the xcex94P target value within the EGR flow controller 36 and a xcex94P error value produced thereby is applied to a proportional-integral (PI) or other known controller 44. An output of controller 44 produces a variable geometry turbocharger signal VGT that is used to control the swallowing capacity and/or efficiency of the turbocharger via any of a number of known techniques via signal path 46. In operation, charge flow to the engine 12, defined for the purposes of the present invention as the sum of fresh air flow into intake conduit 16 and EGR flow into intake conduit 16, is controlled via control of the position of the EGR valve 32 and the pressure differential between the exhaust conduit 30 and intake conduit 16.
One drawback associated with an EGR flow control system 10 of the type illustrated in FIG. 1 is that there exists an interdependency between charge flow and EGR flow such that EGR flow and fresh air flow cannot be controlled separately. Once EGR flow is established by the EGR flow controller 36, the resulting charge flow is defined by whatever fresh air flow is available. System 10 may therefore be optimized for NOx control or for particulate control, but generally not for both. It would accordingly be desirable to provide for an EGR control system wherein EGR flow and fresh air flow may be controlled separately to therefore gain better and more consistent control over the charge flow.